The electromagnetic pure iron has characteristics of low coercive force, high magnetic permeability and excellent processing performance, and is an important functional soft magnetic material.
Traditional electromagnetic iron products are dispatched from factories in a softened annealed state. Only after these pure iron products are stamped into parts and magnetic annealed by the users to eliminate the lattice distortion of cold processing, the products can thus fully show magnetic properties. According to the national standard GB/T 6983-2008, the cold-rolled electromagnetic pure iron steel can be divided into four grades on the basis of the magnetic properties, from high to low: DT4(Hc≤96 A/m), DT4A(Hc≤72 A/m), DT4E(Hc≤48 A/m), DT4C(Hc≤32 A/m). In addition, the magnetic annealing process of electromagnetic pure iron are stipulated as follows: when the annealing is protected by vacuum or inert gases, the electromagnetic pure iron is heated to a temperature of 900±10° C. with the furnace and kept for 1 h, and then the electromagnetic pure iron is cooled to 500° C. or less or room temperature at a cooling rate of less than 50° C./h and then discharged from the furnace; when annealing in a decarburization atmosphere, the electromagnetic pure iron is heated to 800° C. with the furnace, and then heated to 900±10° C. in no less than 2 h and kept for 4 h, and then the electromagnetic pure iron is cooled to 500° C. or less or room temperature at a cooling rate of less than 50° C./h and then discharged from the furnace.
An important application of the cold-rolled electromagnetic pure iron sheet strip is magnetic shielding materials, such as magnetic shell of electrical relay. In the conventional process, the parts are stamped and formed, and then magnetic annealed for up to several hours, the problem is that the magnetic shell parts are always large, which adds extra requirements for annealing equipment, the production capacity is usually limited by the furnace loading capacity, and thereby prone to resulting in making the magnetic annealing process become a bottleneck in the entire production process, which extends the product manufacturing and processing cycle, and increases the cost thereof. Therefore, the manufacturers hope to use the electromagnetic pure iron sheet strip having low coercive force (<100 A/m) and high formability, and does not require further magnetic annealing, but the prior art has not yet reached this target.
Analysis of existing patents related to electromagnetic pure iron products is shown in Table 1. First of all, most of the patents are focused on the continuous improvement of magnetic properties of cold-rolled electromagnetic pure iron, wherein the magnetic properties of the material is improved through the adjustment of alloy composition, the optimization of hot-rolled and cold-rolled process, and the control of magnetic annealing stages. The patent CN103789609A claims a method of improving the purity of electromagnetic pure iron, wherein the impurity element is reduced by electroslag remelting of forging ingot. Patent CN104232856A is directed to the problem that the surface of the workpiece may be easily oxidized during the magnetic annealing process, wherein an improvement method of magnetic annealing the electromagnetic pure iron parts is proposed.
TABLE 1Analysis of related patents of electromagnetic pure iron productsPublicationAlloyNumberCompositionHot-Rolled ProcessCold-Rolled ProcessAnnealing ProcessProductsCN1211625ALow AlHeating 1100-1250° C.—Cover annealing 580° C.DT4EFinal rolling 850-950° C.and kept for 5 h;cold-rolledReeling 600-750° C.Magnetic annealingsheet850-910° C. and kept for 4 hCN1410580Low AlHeating 1000-1250° C.Deformation >60%Continuous annealingDT4EFinal rolling 750-900° C.600-800° C.,cold-rolledMagnetic annealingsheet800-900° C. and kept for 2 hCN1775466High AlFinal rolling 830-890° C.DeformationMagnetic annealingDT4CReeling 680-750° C.30-50%900-980° C. and kept forcold-rolled3-5 hsheetCN103205548AHigh AlFinal rolling 860-1000° C.DeformationCover annealing 540-560°DT4CReeling 700-800° C.30-40%C. and kept for 6-8 h;cold-rolledMagnetic annealingsheet1000-1100° C. and keptfor >2 hPublicationNumberSummary Of The InventionProductsCN103789609AHigh Al (electroslag remelting)→hot-rolled barElectromagneticpure iron barwithout hair seamCN104232856Amagnetic annealing process of the formed parts: 850-900° C., kept forAnnealing method3-4 h, protect with alumina powder to prevent oxidation